I don't normally post on relationships, but really wanted to say something here as I've been through very similar with my exH who pretty much lived a double life with his mistress for well over a year. She had zero clue of my existence (well, she thought he was divorced) and me of hers, until he slipped up. He had brought her to our house, they had shagged in my bed, more than once. He'd gone round hiding photos and so on and claimed any other feminine touches were from when I lived there. I only found out because the fuckwit paid for some flowers for her by card over the phone and the old-fashioned florists posted the receipt to our house, and only put the surname on the envelope not the title. I opened the envelope and there was the receipt, stapled to a copy of the order '30 roses and message "I love you more than words can say, my brave, beautiful girl, love fuckwit xxx' plus (conveniently) her name, and work address, over 60 miles away. I can remember the feeling like concrete in my stomach when I dialled her number, and her reaction. He wasn't home with me that day because he was working miles from home with two overnight stays. Wrong. He wasn't home with me that day because he was on his way to her house, then they were going to a wedding to which they had been invited as a couple. Her friends loved him, thought he was a right charmer, he'd spent nights out and evenings away with her family. He'd even been to Paris with her when I thought he was working in bloody Leeds for 3 days! Seriously, I am an intelligent woman, and he still pulled the wool over my eyes to an astronomical degree.
I was 5dpo after our third round of IVF when I found out. The flowers were, for her, following the termination she'd had the previous week. So literally he took her for a termination one day then came home to me and we went back for the transfer the next day. Neither of us had a CLUE. He was a workaholic, or so we both thought. He had a secret SIM card and phone on which he communicated with her. He told me he had IBS hence having to spend such long sessions on the loo (which was when he was texting her, under the pretence of working in his high flying long hours job). Honestly it was simply unbelievable. I ended up leaving as he refused and the house was in his name. Got a rental flat on a second floor, with an intercom, cut all communication, only dealt with him via a solicitor. I could go on and on and on, what I revealed about him and the extent of his deceit was shocking. I was still finding out stuff months later through other people and not by digging either, things would just come to light.
The fact is that a lot of this isn't actually about YOU (sorry). He's got a massive, massive adrenalin kick from all the lying and skulking about, plotting his next excuse to her, fabricating his next story, concucting his next move. That rush and adrenalin is quite addictive. The getting away with it, the 'winning' at not being caught, that thumping racing heart as his wife walks in the room and he's texting you. He doesn't want to loose you because without you in the game, there is no game. Remove yourself from the game 100%.
It will get better, you will leave this behind, but zero contact all the way. My life now is wonderful.... I hope you are ok and being strong.